Four-stranded DNA: cancer, gene regulation and drug development

DNA can form many structures other than the famous double helix. In particular, guanine-rich DNA of particular sequences can form four-stranded structures, called G-quadruplexes. This article describes the structural form of these sequences, techniques for predicting which sequences can fold up in this manner and efforts towards stability prediction. It then discusses the biological significance of these structures, focusing on their importance in telomeric regions at the end of chromosomes, and their existence in gene promoters and mRNA, where they may be involved with regulating transcription and translation, respectively. Ligands that are capable of selectively binding to these structures are introduced and described, as are DNA aptamers that form G-quadruplex structures; both of these classes of compound have been investigated as anticancer agents in clinical trials. The growing use of G-quadruplexes in the nanotechnology field is also outlined. The article concludes with an analysis of future directions the field may take, with some proposals for further important studies.